In a conventional display device, known is technology of dividing a display screen into a plurality of regions and changing the brightness for each segmented region in order to improve the picture quality of the display panel (for example, refer to Patent Literatures 1 and 2).
Moreover, when a display screen is divided into a plurality of regions and the brightness is changed for each segmented region, a visually unpleasant sensation will arise between the segmented regions. With a conventional display device, in order to alleviate the visually unpleasant sensation between the segmented regions, known is technology of inhibiting the brightness difference between the target segmented region and the peripheral segmented regions (for example, refer to Patent Literature 3).
In addition, with a conventional display device, known is technology of disposing LEDs at the boundary division of the adjacent segmented regions in order to alleviate the visually unpleasant sensation between the segmented regions (for example, refer to Patent Literature 4).
Nevertheless, even if the foregoing technologies are adopted, when pixels (white pixels) of high brightness and pixels (black pixels) of low brightness coexist in the image to be displayed, there is a problem in that it is not possible to display the image at an appropriate brightness.
Specifically, this is now explained with reference to FIG. 40 and FIG. 41. FIGS. 40A to C are diagrams showing a video picture (still picture) that is displayed on a conventional liquid crystal display device when the backlight is set to a high brightness. FIG. 40A is a diagram showing an example of a video picture signal that is input to the display panel, FIG. 40B is a diagram showing the brightness of the backlight to illuminate the segmented region when the video picture signal shown in FIG. 40A is input, and FIG. 40C is a diagram showing the video picture that is actually displayed on the display screen.
In FIGS. 40A to 40C, when a black pixel and a white pixel coexist in the segmented region 101 at the center of the screen, the backlight is set to a high brightness in order to brightly display the white pixel. In the video picture signal shown in FIG. 40A, a white image 102 configured by a white level pixel and a black image 103 configured by a black level pixel coexist in the segmented region 101. The white image 102 is the center portion of the segmented region, and the black image 103 is the peripheral portion of the white image 102.
As shown in FIG. 40B, when a white level pixel and a black level pixel coexist in a single segmented region, the backlight for illuminating that segmented region is lit with high brightness in order to display the white level pixel. Here, the black level pixel is displayed black by lowering the transmittance of the liquid crystal panel. Nevertheless, it is difficult to cause the transmittance of the liquid crystal display element to become completely zero. Thus, light from the brightly lit backlight leaks to the black level pixel, and a so-called “black floating” phenomenon where the black image 103 becomes slightly bright will occur. FIG. 40C is a diagram showing a state where the black floating is occurring.
As shown in FIG. 40C, when the backlight is set to a high brightness, in addition to the region where the white image should be displayed, the region where the black image should be displayed is also illuminated with a high brightness. Thus, a gray image rather than a black image is displayed, and the so-called black floating problem will arise.
FIGS. 41A to 41C are diagrams showing a video picture (still picture) that is displayed on a conventional liquid crystal display device when the backlight is set to a low brightness. FIG. 41A is a diagram showing an example of a video picture signal that is input to the display panel, FIG. 41B is a diagram showing the brightness of the backlight to illuminate the segmented region when the video picture signal shown in FIG. 40A is input, and FIG. 41C is a diagram showing the video picture that is actually displayed on the display screen.
In FIGS. 41A to 41C, unlike FIGS. 40A to 40C described above, when a black pixel and a white pixel coexist in the segmented region 101 at the center of the screen, the backlight is set to a low brightness in order to darkly display the black pixel. As shown in FIG. 41C, when the backlight is set to a low brightness, a black image is displayed in the region where the black image should be displayed. Nevertheless, in the region where the white image should be displayed, a gray image rather than a white image is displayed, and a problem of insufficient brightness will arise.